9. In zones or parts of zones not complying with the air quality limit values laid down in Directive 2008/50/EC, Member States shall assess the need to apply, for individual medium combustion plants in those zones or parts of zones, stricter emission limit values than those set out in this Directive, as part of the development of air quality plans referred to in Article 23 of Directive 2008/50/EC, taking into account the results of the information exchange referred to in paragraph 10 of this Article, provided that applying such emission limit values would effectively contribute to a noticeable improvement of air quality.